This invention relates to antennas, and more especially, to radar antennas such as for use in radar altimeters.
Conventional microwave antennas are of one of two forms: a horn antenna, or a planar or printed element antenna. Horn antennas are relatively large and heavy but produce a good match, that is, the proportion of microwave energy transmitted to that which is reflected by the antenna back into the system is high over a wide range of frequencies. The planar element antenna, however, has a good match at only a narrow range of frequencies, the proportion of reflected energy increasing rapidly at frequencies on either side of the ideal frequency. The advantages of the planar element antenna are that it is very compact, of light weight and relatively easy to manufacture at low cost.